import java.util.Scanner;

public class if3 {

    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        int num1=input.nextInt();
         System.out.println();
        int num2 =input.nextInt();

        int sum = num1 + num2;

        if (sum >= 50) {
            System.out.println("hello world!");
        }
        double num3 = input.nextInt();
        double num4 = input.nextInt();

        if (num3 > 10.0 && num4 < 20.0) {
            System.out.println(num3 + num4);
        } else {
            System.out.println(num3 * num4);
        }

        
        System.out.println("请输入狗的年龄（岁）：");
        int dogAge = input.nextInt();

        if (dogAge < 0) {
            System.out.println("无效的输入：狗的年龄不能为负数。");
        } else {
            int humanAge;
            if (dogAge <= 2) {
                humanAge = dogAge * 10;
            } else {
                humanAge = 21 + (dogAge - 2) * 4;
            }

            System.out.println("您的狗相当于人类的 " + humanAge + " 岁。");
        }

        input.close();
    }
}

